Explain why two flashlights held close together do not produce an interference pattern on a distant screen?

Why can two lamps of the same type not produce interference fringe?

In Young's double -slit experiment butter paper is placed convering one of the slit. How will the interference pattern on a distant screen change if butter paper partially refracts the light through it?

Statement-1: Light from two coherent sources that are not in phase does not produce an interference pattern. Statement-2: Incoherent sources do not produce a sustained interference pattern.

Monochromatic light from a narrow slit illuminates two parallel slits producing an interference pattern on a screen. The separation between the two slits is now doubled and the distance between the screen and the slits is reduced to half. The fringe width

Monochromatic light from a narrow slit illuminates two parallel slits producing an interference pattern on a screen. The separation between the two slits is now doubled and the distance between the screen and the slits is reduced to half. The fringe width